The growing complexity of integrated circuits or microchips has led to a gap between what can be designed and what can be verified in a reasonable amount of time. As a result, there are frequently chips that are designed, manufactured, and then considered unusable. There may be numerous reasons why a chip is deemed unusable or in need of modification, but the most common design faults are: design errors or bugs, performance issues, inoperability and non-compliance to a standard. Often when a chip is deemed unsuitable for use, the chip need only be partially redesigned to correct its design faults. Furthermore, usually only a few logic elements need to be changed to fix the design faults.
Currently when a chip needs modification to fix design faults, designers often have two options. The first option is referred to as a “re-spin”. Typically in a re-spin, the entire layout or blueprint for the chip manufacturing is redone or reassembled. The second option is to use unused logic elements that were placed on the chip, called spare-gates, to fix design faults. Often both options require the chip layout to be rebuilt by the manufacturer, but the use of spare-gates or an Engineering Change Order (ECO) is often a more attractive option in terms of cost as only a few metal masks usually need to be rebuilt as opposed to a change of the entire mask set for a re-spin. This usually saves time and money compared to a full re-spin. However, an ECO can handle only a finite number of changes and so the decision may depend on the amount of logic that needs changing.